In recent years, silicon carbide has been increasingly employed as a material for a semiconductor device such as a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) in order to allow a higher breakdown voltage, lower loss and the use in a high-temperature environment and the like of the semiconductor device. Silicon carbide is a wide band gap semiconductor having a band gap wider than that of silicon which has been conventionally and widely used as a material for a semiconductor device. By employing the silicon carbide as a material for a semiconductor device, therefore, a higher breakdown voltage, lower on-resistance and the like of the semiconductor device can be achieved. A semiconductor device made of silicon carbide also has the advantage of exhibiting less performance degradation when used in a high-temperature environment than a semiconductor device made of silicon.
For example, Brett A. Hull et al., “Performance of 60 A, 1200V 4H—SiC DMOSFETs”, Materials Science Forum, Vols. 615-617, 2009, pp 749-752 (NPD 1) discloses a MOSFET including an n type drift layer formed on a silicon carbide substrate, a pair of well regions, and a gate insulating film. According to the MOSFET disclosed in this document, switching energy loss is 9 mJ at the time of switching from an on state where a drain-source current is 65 A to an off state where a drain-source voltage is 750 V.